Impact toughness of weldments in Al-Mg-Si alloys

6000 series Al-Mg-Si alloys are frequently used for welded structures. The present investigation is conducted to evaluate the level of mechanical properties, especially impact toughness of welded Al-Mg-Si alloys with different amounts of Mn addition and using two types of fillers Al-Si (A4043) and Al-Mg (A5356), respectively. Particular attention is paid to the effect of microstructure on toughness. As one of the most important characteristics of a structural material, toughness is evaluated by the instrumented Charpy impact test method. When Al-Mg filler is used and Mn is not added, recrystallization occurs in the heat affected zone (HAZ), however, recrystallization can be suppressed by a small amount of Mn addition. The structure having large coarsened recrystallized grains is more susceptible to liquation crack that is detrimental to the mechanical properties, especially toughness. The results obtained show that toughness of the welded metal can be improved 20-30% by adding Mn. Using A4043 filler, the level of absorbed energy decreases as the content of Mg increases, and low Mg and without Mn addition results in a good combination of the mechanical properties. However, using the A5356 filler, the level of absorbed energy increases as the content of Mg increases and decreases as the Si content increases. In this case, the highest value of absorbed energy was recorded for alloy 8 (0.7%Mn). When A5356 filler is used, the toughness is about 56% higher than using A4043 filler.